The present invention relates to converter steel production by top blowing of oxidizing reactants delivered to the initial materials and more specifically to tuyeres for introducing reactants into a bath of molten metal. Commonly used as oxidizing reactants in this case is gaseous oxygen introduced alone or in a mixture with powder materials.
The term "bath of molten metal" as used hereinafter denotes a mass of molten metal which can be liquid cast iron, and the "particulate materials" mean scrap and slag-forming additives, such as lime, slag forming materials and the like additives.
Widely known in the art is a tuyere for introducing oxygen into a bath of molten metal consisting of an elongated water-cooled casing through a bore of which a flow of oxygen with powder materials is being fed. At the outlet, the casing internal surface is given the shape of a cone diverging towards the outside and forming thus a cooling shield. Installed at the outlet from the casing before the cone-shaped portion there is a replaceable stopper provided with nozzles and made of a heat-proof material.
The water-cooled tapered portion of the tuyere casing gives the stopper protection against splashing slag and metal. On a side surface of the stopper facing the casing there is an annular collar resting on a split ring which consists, for example, of four parts disposed on a corresponding annular collar provided on the internal surface of casing.
To replace the stopper, it is displaced into the casing bore so as to become separated from the parts of split ring, said parts are withdrawn and then is withdrawn the stopper from the casing. To insert a new stopper, the procedure is repeated in the reverse order.
To simplify the job of replacing said stopper, it must easily fit the split ring. This fact and also the presence of unavoidable clearances at contact between the stopper, parts of ring and casing are likely to bring about leaks of oxygen through said clearances with the result that the rate of blast will be changed. Furthermore, the introduction of particulate materials in conjunction with oxygen through narrow nozzles of the stopper is a problem by itself.
Further known is a tuyere in which particulate materials are introduced through a separate co-axial pipe immovably installed in the casing bore. Said tuyere has a replaceable stopper with nozzles threadedly attached to the casing at the outlet. In this case, the replacement of a damaged stopper is a problem due to the danger of damaging the thread exposed to high temperatures in the reaction zone. Also nozzles of the stopper are likely to be blinded to splashing slag and metal.
Finally known is a tuyere for blowing oxygen through cast iron which consists of an elongated water-cooled tubular casing disposed wherein is also a co-axial pipe. Oxygen is introduced through said tuyere in two flows at different pressures. While fed through the casing is oxygen at low rate of flow and pressure, blown through the pipe is oxygen at high rate of flow and pressure with or without finely-ground materials in the form of suspension. The oxygen introduced through the casing at low rate of flow and pressure brings about frothing of slag and improves dephosphorization. Also the blowing with oxygen under low pressure allows to increase the amount of scrap in the charge. On the other hand, the excessive frothing of slag occuring at low rates of flow and pressures of oxygen blasting must be suppressed from time to time by interrupting the outflow of oxygen through the annular clearance in casing bore. This, however, invites blocking of said clearance by the material of bath. To prevent the blocking, the annular opening in the casing is fitted with a stopper made of a heatproof material and provided with pores or small holes with a diameter between 0.2 and 5 mm to enable the oxygen to flow. The presence of stopper does not eliminate the possibility of blinding holes by the material of bath and for this reason said stopper must be replaced by a new one from time to time. The stopper is a tight fit into the outlet from tuyere casing and its replacement without breaking or damaging the casing wall is a problem.